Exhaust driven turbochargers include a rotating group that includes a turbine wheel and a compressor wheel that are connected to one another by a shaft. The shaft is typically rotatably supported within a center housing by one or more bearings (e.g., oil lubricated, air bearings, ball bearings, magnetic bearings, etc.). During operation, exhaust from an internal combustion engine drives a turbocharger's turbine wheel, which, in turn, drives the compressor wheel to boost charge air to the internal combustion engine.
During operation, a turbocharger's rotating group must operate through a wide range of speeds. Depending on factors such as size of the turbocharger, the maximum speed reached may be in excess of 200,000 rpm. A well balanced turbocharger rotating group is essential for proper rotordynamic performance. Efforts to achieve low levels of unbalance help to assure shaft stability and minimize rotor deflection which in turn acts to reduce bearing loads. Reduced bearing loads result in improved durability and reduced noise (e.g., as resulting from transmitted vibration).
To reduce vibration, turbocharger rotating group balancing includes component and assembly balancing. Individual components such as the compressor and turbine wheel assembly are typically balanced using a low rotational speed process while an assembly is typically balanced using a high speed balancing process. In general, such an assembly includes a housing (e.g., a center housing) and is referred to as a center housing and rotating assembly (CHRA).
Various balancing concerns stem from CHRA design, particularly characteristics of components that can dictate order of assembly. For example, many center housings are configured to receive a bearing via a compressor side opening and to receive a shaft via a turbine side opening. In such configurations, it makes sense to balance the shaft and the bearing once they are properly positioned in a center housing (e.g., as a CHRA). In other words, balancing a shaft and a bearing as an assembly (e.g., set in a jig) prior to insertion into the center housing does not necessarily ensure proper balance once these components are inserted into the center housing to form a CHRA. For example, where a press-fit is required between a race or rolling elements of a bearing and the shaft, it can be difficult to un-press-fit, insert in the components into center housing and re-press-fit the bearing and the shaft while achieving an exact realignment.
Various technologies described herein pertain to assemblies that include a sleeve where the sleeve may be, for example, configured to support a bearing and shaft subassembly and to fit into a center housing. Such an approach can optionally facilitate balancing, minimize balance-related noise, vibration and harshness (NVH), etc. Such an approach may enhance stocking, manufacturing, inspection, maintenance, repair, and replacement (e.g., with components having same or different characteristics).